β-galactoside-α-2,6-sialyltransferase2 Ovcrexpression Is Associated With Poor Prognosis And Induces Tumor Development In Breast Cancer

Breast cancer is the most common cancer among women worldwide and stays one of the leading causes of cancer death. Despite some progress has seen in the field of breast cancer research, the diagnosis and treatment of breast cancer are still unfavorable so far, leading to unsatisfactory prognosis and high mortality. Therefore, novel targets for diagnosis and treatment for breast cancer has yet to be discovered. β-galactoside-α-2,6-sialyltransferase1 (ST6Gal1) is one of the best known sialytransferase which has been shown by many publications that it is highly expressed in many types of malignancies including breast cancer and plays an important role in tumor development and invasion. As an isoenzyme of ST6Gal1, recently ST6Gal2 has been characterized, however its function in tumor development or tumor invasion has not been clarified yet.To study the potential function of ST6GAL2 enrolled in the regulation of breast cancer, we performed Real-time PCR (RT-PCR) and immunohistochemical stain to detect the expression levels of ST6GAL2 in both tumor tissue and normal tissue of the 40 clinical breast cancer samples. Gene expression profile of 778 BC patients was downloaded from The Cancer Genome Atlas (TCGA) and analyzed:We divide patients into ST6Gal2 high expression group and ST6Gal2 low expression group, and the association between ST6Gal2 expression and pathological parameters such as tumor stage, ER, PR or HER2 profiles and patients’ age was measured by Fisher Exact Test. Also, the correlation between ST6Gal2 expression and patients’survival time was analyzed by Log-rank test. Subsequently, the expression level of ST6Gal2 of five breast cancer strains was detected by Western Blot and the expression of ST6GAL2 in two relatively ST6Gal2 higher expression breast cancer strains was silenced by siRNA. RT-PCR and Western Blot was performed to validate the effect of siRNA silence. Cell proliferation and cell cycle were analyzed via CCK-8 assay and flow cytometry. Also, adhesion and invasion were detected by a fibronectin-coated 12-plate microplate and Transwell assay. In order to clarify the mechanical bases, we performed gene set enrichment analysis (GSEA) to analyze the correlation between elevated ST6Gal2 expression and elevated expression of genes pertaining to adhesion and metastasis gene set. Western blot and RT-PCR were used to analyze the expression level of genes linked to adhesion and metastasis pathway in breast cancer cells.We found that ST6GAL2 expression level was higher in BC tissues compared with normal adjacent tissues via both RT-PCR and immunohistochemical stain. We analyzed the data from TCGA and found higher expression of ST6Gal2 was positively correlated to aging and HER2 positive status. Importantly, elevated expression of ST6Gal2 was positively correlated to worse prognosis. We detected the expression level of ST6Gal2 in five breast cancer strains and found MCF-7 and T47D expressed relatively high ST6Gal2. We subsequently tested the in vitro function of ST6GAL2 by silencing the gene expression in MCF-7 and T47D. Silencing ST6GAL2 inhibited cancer cell proliferation by arresting cell cycle arrest in G0/G1 phase and dampened cell adhesion and invasion. A GSEA analysis revealed that ST6GAL2 was positively correlated with the elevated expression of genes pertaining to the gene sets of focal adhesion and metastasis. Further Western Blot and RT-PCR showed Silencing ST6GAL2 inhibited expression of RhoA, TGF-β3,VEGFC, CTNNB1,FUT8 as well as WISP-1, all of which play a crucial role in breast cancer metastasis and invasion.In summary, just like its counterpart ST6Gall, ST6gal2 might play an important role in tumor invasion and thus lead to an inferior prognosis in breast cancer patients. These findings indicated that ST6GAL2 might serve as a useful potential target for treatment or a prognosis predictor of breast cancer.